NQC - I'm sooo over dresses and skirts and other impractical things, so I'd wear black or grey trousers and a colourful or (discreetly) sparkly long-sleeved top. Heels. Lots of make-up and def.not an alcohol-nose.
What have you got already that you think would be good? What do you mean by butch, broad shoulders? If so then wide strapped top or halter neck , a A line skirt that skims over the hips could be flattering. I think that trousers and sparkly top would look good too, as you'll be sitting down to drinks food etc I think a really good top half and shoes.
Things I have that fit that might work: - long satiny black skirt - weird black next top with cutouts - clingy red and black and white top - cowl neck tops (black, dark turquoise, brown) - halter neck dress (knee-length cotton, with embroidery) - halter neck dress (knee-length satin, with gems) - black flarey trousers - sequinned vest top type thing - green chinesey sort of jacket - silk dress with lovely flarey skirt with stars on it (ok, I lie, this is too big, must get it fixed ...)
By butch, I mean, I don't really wear makeup, I don't really 'do' my hair (although this year, at least I have some). Also wide shoulders, not that much norkage, big hips and butt, decent legs.
You've great stuff in your wardrobe and you're a natural beauty, if you don't bother with make up, you fit that category for me. Your halterneck dresses sound like they might be nice as they have a bit of embellishment on them. The satiny black skirt would work with the next top or the cowl neck tops if they are made of a fabric that sits well the satin, ie not too heavy. Sequinned top and flarey trousers, sounds great too. The Jacket could look great with the trousers and a strappy top? You've got a whole shop to choose from!